HP Forum Archive 08

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9825A printer Message #1 Posted by Achim on 20 May 2002, 5:02 a.m. Has anyone experience in repairing the 9825A build in thermal printer? In one of my machines some material on the driving solenoid has become sticky and as a result the paper is not transported. I have already removed the printer from the machine and would appreciate some further disassembly instructions and hints for replacement material. Thanks, Achim

Re: 9825A printer Message #2 Posted by Tony Duell (UK) on 20 May 2002, 6:12 p.m., in response to message #1 by Achim I've taken the 9825 printer totally apart (and the 9815 one which is essentially the same). IIRC, you remvoe it from the machine, and take it off the metal bracket (you've done that, right?). Then Undo a screw at each side to release the rectangular metal bar that holds the springs (in metal cups) that press the printhead against the paper. Watch out, this is spring-loaded!. Then remove the bar, cups and springs. Remove the printhead and its heatsink carefully (it's a delicate ceramic hybrid circuit that you will _not_ find a replacement for). Take off the paper-out sensor next (PCB on top, 2 screws). Then take off the right hand sideplate (screws on the side -- again watch out for a spring -- this time the return spring for the solenoid armature). Remove the platten/armature assembly and the solenoid. I think you can remove part of the paper guide by undoing some screws on the left, but it's rarely needed. The manual feed knob pulls off the end of the platten (carefully!) which releases the armature. Don't do this unless you have to -- there's a delicate plastic ratchet inside. The nomrmal trouble is that the damping foam on the armature turns to glue. Clean it off. It isn't essential to the operation of the printer, but you can replace it with any thin foam if you want to. If it still sticks, try sticking a piece of thin paper on the face of the armature to prevent residual magnetism from holding the armature to the solenoid.

Re: 9825A printer Message #3 Posted by Achim on 21 May 2002, 3:23 a.m., in response to message #2 by Tony Duell (UK) Tony, thank you very much for your advice. Yes, I've already unmounted to printer but being aware of the spring-problem I didn't want a disassembly ending up in a mess of parts flying around. I'll try to disassemble the printer according to your description.

Re: 9825A printer Message #4 Posted by W . Bruce Maguire II on 21 May 2002, 4:29 p.m., in response to message #2 by Tony Duell (UK) Tony: I've just been too busy to keep up with the MoHPC forum, but I did glance today and I saw your response regarding disassembling the 9825A printer. If it weren't so trite, I'd say "You're the man!" But I won't say that... How about this: you are 50% Spock and 50% Scotty! Incredibly deep knowledge with the right amount of good-ol' engineer thrown in! ;-) Bill and Dave would be proud! Bruce.

Re: 9825A printer Message #5 Posted by Tony Duell (UK) on 21 May 2002, 6:37 p.m., in response to message #4 by W . Bruce Maguire II Thanks for the compliment! I hope everybody realises, though, that that 'deep knowledge' came from good old engineering as well. I've never worked for HP, I don't have access to 'secret HP manuals'. Instead I take apart and investigate just about everything I own. The reason I can tell you how to take a 9825 printer apart is because I've taken mine apart (and reassembled it). The reason I can tell you the differences between a 33E and 33C PSU board is because I've had both on the bench and I've compared them. While some o you look for 'new in box' calculators, I scrounge all the broken and beat-up ones I can to take to bits. Even 'modern' ones that I don't have a hope of fixing (and for whcih the first attempt at dismantling is likely to do more damage -- that's why I grabed a 48 with cracked display recently...)

Re: 9825A printer Message #6 Posted by Achim on 22 May 2002, 5:19 a.m., in response to message #5 by Tony Duell (UK) Yes, you are right. It makes most of the thrill to get a damaged, ugly looking machine up running and looking rather like new. I made this excerience last year when I got three heavily damaged 9810A. After 'reanimating' my whole knowledge of the '70s about TTL logics, consulting old TI Pocket Guides, and studying the schematics in the patent describing the 9810A, I succeeded in repairing about 10 logic boards and brought two machines back to life. What a moment after some ten hours of work! Achim

Re: 9825A printer Message #7 Posted by Achim on 21 May 2002, 5:41 p.m., in response to message #2 by Tony Duell (UK) Tony, I disassembled the printer according to your excellent instructions and replaced the foam with some 1mm thick self-adhesive felt material. After reassembly I connected the printer to the calc and made some test prints. I noticed that the spacing between each line of dots is about double as normal, whcih results in about double high characters. Could this be a cause of the damping material or an electrical problem? THX, Achim

Re: 9825A printer Message #8 Posted by Tony Duell (UK) on 21 May 2002, 6:05 p.m., in response to message #7 by Achim It's unlikely to be an electrical problem. Most likely the new damping material is thinner than the original, so the armature can move further. The pawl then moves back by 2 teeth on the ratchet and pulls the roller round twice as far when the solenoid is energised. On most of these printers there's an adjustable back stop for the armature. On the front, at the right hand side, look for a screw-slotted pin which carries a stop for the armature. Screw this in a bit -- if you screw it in too far then the printer won't feed paepr at all. Experiment a little with it.

Re: 9825A printer Message #9 Posted by Achim on 22 May 2002, 5:07 a.m., in response to message #8 by Tony Duell (UK) Tony, yes, I also thought that the cause is in the thinner material. There is also a back stop screw which presses against another foam block glued on the plastic part of the armature. This foam block is not sticky degraded but partly irreversable compressed. Maybe I have to replace this one also. Achim

Re: 9825A printer Message #10 Posted by Achim on 23 May 2002, 5:17 p.m., in response to message #8 by Tony Duell (UK) Tony, after I replaced the foam block behind the back stop the paper transport works like it should. I took a piece of 4mm thick self adhesive foam.

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